The invention relates to a method, system and computer program product for reconstructing a model of an object of projection data advantageously gathered by X-ray imaging. It is characteristic for the invention, that after a point of at least one object of interest from at least two projection images is marked as a seed point, where said point locates inside the object of interest in the corresponding projection image, the model of the object of projection data is reconstructed by adding plurality of elementary object elements around the marked seed point in each direction until a criteria, such as likelihood criteria, is fulfilled in said direction, where priori information relating to the object of interest is connected with said elementary object element.